This invention relates to thermal control of solid state electronic devices, and more specifically to the control of temperature of such devices by use of external heat and external chilling.
Solid state electronic components are frequently susceptible to temperature-induced changes in their response. In addition to ambient temperature effects, many solid state devices generate significant amounts of heat during their operation, further complicating such temperature-related problems.
In order to overcome these problems, circuit designers will often specify solid state devices with increased temperature ranges of operation, at considerably higher costs. Other attempts to extend operating temperature range have employed multi-slope biasing and adjustments of sensing threshold levels.
Bubble memories have received attention as a result of the ability of the bubble memory to provide non-volatile memory capacity and because of the rugged nature of bubble memories over other non-volatile memory systems. Bubble memories, however, have been limited in their application as a result of temperature sensitivity.
Referring to FIG. 1, a typical bubble memory has upper and lower limits of operation which change significantly as a result of changes in temperature. In the example given, the upper limit of operation is indicated by the curve U and the lower limit of operation is indicated by the curve L. As can be seen, a safe field bias at one temperature may be out of range at another temperature. Referring to FIG. 2, since threshold levels for a typical bubble memory tend to vary, particularly at the "1" logic level. The "one" level decreases to approach the "0" logic level at higher temperatures within the rang of operation of the bubble memory. A sense threshold, at which circuitry distinguishes between the "0" and "1" logic levels is therefore established at a level which is slightly greater than the "0" logic level in order to obtain a maximum range for the bubble memory.
Referring again to FIG. 1, the establishment of a bias level for extended temperature ranges is more difficult. A conventional bias level would exceed the upper limit of operation at very low and very high temperatures. Therefore, a multi slope bias is chosen, in which the bias is adjusted for temperature in order to follow, to the extent practical, the multi slope bias curve shown in FIG. 1.
In order to reduce temperature effects, heat sinking and thermally controlled environments are used in order to attempt to maintain the solid state device at an appropriate temperature. The provision of such environmental temperature controls imposes some restriction on the use of a circuit which includes the bubble memory, thereby reducing its convenience.
Accordingly, it is an object of a present invention to provide a method of controlling temperature of a solid state device in order to efficiently bring the temperature of the solid state device within an acceptable range. It is a further object to provide a temperature control system for a solid state device which is convenient to operate and is adaptable to a wide variety of environmental conditions. It is a further object of the present invention to provide a system using a bubble memory which is suitable for use in a wide variety of ambient conditions. It is a further object of the present invention to provide a system having a non-volatile memory which is light in weight and which is durable. It is a further object of the present invention to provide a system having a compact readily accessible randon access memory. It is further object of the present invention to provide a bubble memor in which costs are reduced by readily maintaining the bubble memory within a desired temperature range.